The proposed experiments will use physiology to measure single-neuron responses to classical visual illusions, which have been studied by psychophysicists, computational scientists, and occasionally by physiologists, but have never been as systematically or as quantitatively examined as in the proposed experiments. Optical illusions are key to understanding how the brain extracts information from its sensory inputs-if the brain simply recorded all its sensory inputs slavishly, we would not perceive illusions. Instead the brain extracts information from the environment using computations and assumptions;optical illusions are "mistakes" the brain makes that reveal the nature of these computations and assumptions. This systematic approach will narrow the gap between perception and single-unit response properties. We postulate that the physiological correlates of the perceptual phenomena of these various illusions will originate with single-cell properties including center-surround interactions, end-stopping, length summation, or cross-orientation and junctional interactions. However, direct figural reverse correlation mapping can show any other possible mechanisms involved that have not been observed before, in particular ones that are dependent on the special configuration of each illusion and therefore never specifically explored before. The goal of this project is to find out how the way neurons respond to each part of the image reflects the corresponding illusory percept and to find out whether there is a systematic correlation between the response to the illusion and the low-level receptive-field properties of each cell. Comparing maps of activity in both V1 and V2 will enable us to broaden our understanding of the roles of these two visual areas in perception. PUBLIC HEALTH RELEVANCE Understanding how single neurons respond to well studied visual illusions will yield insights into how the brain processes visual information particular and, because the visual system is a model system for understanding how the brain works, it should also provide insights into human cognition. There are neurological and psychiatric conditions in which selective aspects of visual processing are impaired, such as the agnosias, as well as schizophrenia and autism;therefore ultimately our understanding of how the normal brain processes these illusions will inform our understanding of these conditions.